Update README.md

Author: hyunwoongko

README.md

@@ -770,7 +770,7 @@ split_morphemes(
     - `drop_space=True`: drop all space characters in output (default)
     - `drop_space=False`: remain all space characters in output
 - **return_pos: Return pos information or not**
-    - `return_pos=True`: return results with pos information
+    - `return_pos=True`: return results with pos information (default)
     - `return_pos=False`: return results without pos information
 </details>